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GCSE Maths / Edexcel

Percentage increase and decrease

Increase or decrease an amount by a percentage using percentage multipliers or by finding the percentage change first.

Number and Place ValueFoundation and HigherGrades 4 to 6Focused skill

Curriculum path: GCSE Maths > Edexcel > Number > Percentages > Percentage increase and decrease

Pearson Edexcel GCSE Maths number: solve percentage increase and decrease problems.

Practise this topicUpload your answerAsk AI to explain thisTry exam-style questions
Revision notes

Theory, examples, and quick checks.

Keep the method short, then practise straight away. This note is written for GCSE Maths Edexcel students who need clear working and reliable method marks.

Theory

Percentage increase means the amount gets bigger.

Percentage decrease means the amount gets smaller.

One method is to find the percentage amount first, then add or subtract it.

A quicker method is to use a multiplier. A 15% increase means 100% + 15% = 115%, so multiply by 1.15.

A 20% decrease means 100% - 20% = 80%, so multiply by 0.80.

For exam questions, write the multiplier or show the percentage you add or subtract so the method is clear.

Key ruleIncrease multiplier = 1 + percentage as a decimal. Decrease multiplier = 1 - percentage as a decimal.

Worked examples

Percentage increase

Increase 80 by 15%.

  1. 15% increase multiplier = 1.15.
  2. 80 x 1.15 = 92.

Answer: 92

Percentage decrease

Decrease 150 by 20%.

  1. 20% decrease leaves 80%.
  2. 80% = 0.8.
  3. 150 x 0.8 = 120.

Answer: 120

Find then add

Increase 60 by 25%.

  1. 25% of 60 = 15.
  2. 60 + 15 = 75.

Answer: 75

Common mistakes

  • Using 0.15 instead of 1.15 for a 15% increase.
  • Adding the percentage number instead of the percentage amount.
  • Using 1.20 for a 20% decrease instead of 0.80.
  • Finding 20% correctly but forgetting to subtract it.

Quick exercise

Try these before moving to the exam-style questions.

  1. Increase 100 by 15%.
  2. Increase 80 by 25%.
  3. Decrease 200 by 10%.
  4. Decrease 150 by 20%.
  5. Increase 250 by 12%.
Exam-style questions

Practise the same skill at three levels.

These are original GCSE-style questions with mark schemes, common wrong answers, and AI marking guidance so feedback stays close to exam expectations.

Basic GCSE styleFoundationNon-calculator2 marks

Increase 60 by 20%.

percentage increasepercentagesfoundation number
Standard exam styleFoundation and HigherCalculator3 marks

A laptop costs 480 pounds. In a sale, the price is decreased by 15%. Find the sale price.

percentage decreasemultipliersmoney context
ChallengeHigherCalculator4 marks

A population increases by 12% in one year and then decreases by 15% the next year. The starting population was 2500. Find the final population.

successive percentage changemultipliershigher reasoning